In the operation of a resonator fiber optic gyroscope (RFOG), there is often a need to suppress either the optical carrier or certain sidebands of the modulated-light beam to reduce errors caused by optical interference. This interference may take place between co-propagating or counter-propagating lightwaves due to back reflections in the resonator. For gyros to achieve good performance it is critical to maintain high level of suppression of a selected frequency component over long periods of time. However, due to environmental influences, it is often hard to stably maintain suppression of selected sidebands or of the carrier frequency of a modulated optical wave.